Conventionally, in an engine valve that demands wear resistance, Co-based hard-facing alloys such as Co—Cr—W—C alloy represented by Stellite (registered trademark) and Co—Mo—Si alloy represented by Tribaloy (registered trademark) are widely used, and in some engine valves, Ni-based hard-facing alloys (Patent documents 1 to 3) and Fe-based hard-facing alloys (Patent documents 4 to 8) are applied or examined.
The Co—Cr—W—C alloy has an insufficient wear resistance though having a high impact resistance as a hard-facing alloy, so that the alloy cannot withstand use for a long period of time. Also, the Co—Mo—Si alloy has an insufficient impact resistance though having a high wear resistance as a hard-facing alloy, so that problems such as cracks and exfoliation accompanied thereby are raised. Further, the Co—Cr—W—C alloy and the Co—Mo—Si alloy are made up of Co and Cr, W or Mo, therefore, the content of rare metals cannot be controlled so as to lower.
On the one hand, Ni-or Fe-based hard-facing materials having properties equivalent to the Co—Cr—W—C alloy and the Co—Mo—Si alloy have been developed and used (Patent documents 1 to 8), however, in the engine valve which is used under increasingly harsh environment, there is a problem that all of wear resistance, impact resistance and hot corrosion resistance cannot be satisfied.